We have isolated and identified a compound of plant origin, 6-methoxybenzoxazolinone (6-MBOA), which functions as a reproductive stimulant in Microtus montanus. To date this compound has been studied in the laboratory in females and in breeding pairs. The aim of this proposal is to examine the effects of 6-MBOA on male Microtus in terms of growth, onset of sexual maturation and testicular responses under different photoperiod regimes. Animals will receive the compound by injection, mixed in the diet or implanted in silastic capsules in the abdominal cavity. Evaluation of responses will be made by assessing testicular hypertrophy, histology of the testis and epididymis, and the blood plasma testosterone level (by radioimmunoassay). A breeding experiment in which either the male or the female in the breeding pair is implanted with 6-MBOA will enable us to accurately assess each sexes' contribution to the increased breeding performance observed when both sexes received the compound. A compound that can function to regulate and stimulate male reproductive responses would be invaluable in terms of human fertility and productivity of livestock.